An ultrasonic imaging apparatus measures an ultrasonic reflectance of the tissue in an object with ultrasonic waves. In general, the ultrasonic imaging apparatus displays an ultrasound image of the reflectance of a diagnostic portion with the measured value, as luminance. Recently, in the ultrasonic imaging apparatus, time-series images of the temporal change in the tissue are obtained upon applying a pressure to the measured portion, the correlation between the time-series images is obtained, the amount of motion (e.g., displacement) of the tissue is obtained, the strain of the tissue is measured by spatially differentiating the amount of motion, and an elastic modulus of the tissue is measured for tissue diagnosis. Further, the measured strain or the distribution of elastic moduli is displayed as an elastic image.
The elastic image, serving as the strain or the elastic modulus, is displayed as a color image added with information on the hue of red, blue, and the like, depending on the amount of strain or the elastic modulus of the tissue. That is, the tumor spread or tumor size is easily diagnosed by displaying an image that is obtained by adding, mainly, a specific color to a hard portion of the tissue. As disclosed in Patent Document 1 and Patent Document 2, the elastic images, serving as color images, are arranged on the same screen as that of a B-mode image, or are overlaid to and are displayed on the B-mode image, as mentioned above. In particular, Patent Document 2 proposes that the elastic images are displayed by varying the luminance of red, blue or another color, depending on the elastic modulus.
However, in the ultrasonic imaging apparatus disclosed in Patent Document 2, the color assignment is not considered upon setting the strain or the elastic modulus as color images. In general, in order to display a physical quantity, such as the distribution of temperatures, by varying the hue for the purpose of easy understanding, the temperature within a display range from the minimum value to the maximum value thereof is classified to a plurality of segments. The colors from red to blue via a neutral color corresponding to the segments are assigned by varying the hue in view of tone.
The elastic image is used for diagnosing the tumor, such as cancer. However, the shape and the hardness of the tumor, such as the cancer, are varied depending on individuals, portions, and medical conditions.
Therefore, the uniform fixing of the hue corresponding to the level of strain or elastic modulus necessarily causes the diagnosis of the portion size with a predetermined hardness or more. Thus, the diagnosis takes a long time, the boundary of the tumor cannot be easily identified, and there are above-mentioned problems of deterioration in convenience. In particular, there is a risk that it is impossible to accurately determine the range of the affected part to be extirpated.    Patent Document 1: JP 5-317313A    Patent Document 2: JP 2000-60853A